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Thursday, August 9, 2018

Three cheers for the Tree Sparrow!

This is an entertaining book. Really. The author, J.
Denis Summers-Smith, has spent 50 years studying sparrows. You heard me. He has
been studying *sparrows* for 50 years. Apparently, they even call him Sparrow
Man. The man has visited far-away places such as Siberia, Afghanistan and Iran
with the sole purpose of observing sparrows! This is his fourth book on this
rather obscure subject.

"The Tree Sparrow" is essentially a mini-encyclopaedia about the Tree
Sparrow, one of the 25 species of sparrows. It's not suited for the general
reader, being filled with detailed and somewhat technical information. Rather,
it's a reference work for ornithologists and (perhaps) advanced bird-watchers.

Still, I found the book interesting, in a strange kind of way. I'm one of those
"bad bird-watchers", after all. Here in Sweden, telling the
difference between House Sparrows and Tree Sparrows is considered common
knowledge. It's something every child learns already in preschool, or even
earlier. At least in the suburbs of Stockholm, both sparrows can be seen, often
in mixed flocks. Tree Sparrows are so small that I often fear accidentally stepping
on them and crushing them whenever I take a walk through suburbia! Confusingly,
the Tree Sparrow is called "Willow Finch" in Swedish.

From Sparrow Man's book, I learned that the Tree Sparrow is a colonial and
social species. Unusually, both sexes look almost identical. To get a
competitive advantage over other small passerines, the Tree Sparrows choose and
defend a potential nesting site long before the actual breeding season. Another
strategy is to attack and take over completed nests of other songbirds,
destroying their eggs in the process! Great Tits and Blue Tits can be attacked
in this way. Even in mixed species flocks, Tree Sparrows aren't the subordinate
species, but fall somewhere in the middle of the dominance hierarchy. (I had
expected these micro birds to be the pushovers of the bird world!) Of course,
Tree Sparrows might get attacked by larger birds.

The Tree Sparrow's main competitor is the House Sparrow, a similar but sturdier
species. House Sparrows are dominant over Tree Sparrows. For instance, House
Sparrows always take higher-placed nest boxes, leaving lower-placed nest boxes
(where the danger of predation by snakes and weasels is greater) to Tree
Sparrows. If all nest boxes are placed low, House Sparrows attempt, with varied
rates of success, to displace their smaller cousins altogether. Both prefer
urban settings, but apparently "this town aint big enough for both of
us". In areas where both species are represented, the House Sparrow lives
in the cities, while the Tree Sparrow is forced to become a suburban or even
rural bird. In East Asia, where there are no House Sparrows, the Tree Sparrow
has become an urban species. In parts of Siberia, both species are relatively
new, and still compete with each other in the Siberian towns, while in
Afghanistan, the Tree Sparrow have somehow forced the House Sparrow to become
the rural species. (Since House Sparrows usually never loose against the
smaller Tree Sparrows, some have suggested that the meek Afghan House Sparrow
must be a separate species.) Despite this intense competition, the two species
occasionally interbreed. Photos of these hybrid sparrows are included in the
book. The author believes that interbreeding takes places in areas where both
species are rare. Rather than giving up breeding altogether, Tree Sparrows who
can't find a mate, pair bond with House Sparrows. The hybrids are viable, but
it's not clear whether they are really fertile. (Some other hybrid sparrows
are.)

From the book, we further learn that Tree Sparrows have a staggeringly high
mortality rate. 20% make it to their first breeding season, and only 4% are
alive by the second breeding season. Predation by raptors and cats is common,
and pesticides can be another threat. Ironically, when Sparrowhawks were
decimated by pesticides in Britain, the number of Tree Sparrows started
climbing. In China, humans kill Tree Sparrows and export them to Italy, where
they are eaten! 60 years ago, the untractable Chairman Mao even ordered an
extermination campaign against Tree Sparrows, ordering every citizen in China
to participate. Millions of sparrows were killed in the belief that this would
increase rice yields. It didn't. Apparently, the poor sparrows didn't live
exclusively on rice grains. Another great victory for Marxism-Leninism-Mao
Zedong Thought?

What I find most fascinating with books of this kind, are the little pieces of
truly weird information. Thus, we learn that Tree Sparrows once nested in a
hollow coconut on an island outside Thailand (the author saw it happen - he
actually visited Thailand to study breeding Tree Sparrows). Or that a small
group of these sparrows somewhere in Europe actually laid their eggs in the
lower part of a Rook's nest, while the Rook was still using the upper part. In
another strange case, the care of a parasitic Cuckoo chick reared by Wagtails
was taken over by Tree Sparrows! It's unclear whether the Tree Sparrows
attacked the Wagtails in order to take over their nest, only to be mesmerized
by the Cuckoo? Sometimes, crime really doesn't pay...